(a) Field
The present invention relates to a photodetector and an image sensor. Particularly, the present invention relates to a photodetector using surface plasmon resonance and an image sensor.
(b) Description of the Related Art
A known photodetector senses light by using a semiconductor device. A wavelength region of sensed light is determined according to band gap energy of the used semiconductor device. That is, light having energy that is higher than a band gap of the semiconductor device excites electrons of a valence band to a conduction band to change an electrical characteristic of the semiconductor device. Thereby, light is sensed. Accordingly, light having energy that is lower than band gap energy of the semiconductor device is not capable of being sensed. Therefore, in the case of silicon, it is impossible to sense light having a wavelength that is larger than 1.1 μm in an infrared light region.
Band gap energy needs to be adjusted to change the wavelength of light capable of being sensed. A method for doping an impurity or a method for using a semiconductor device of another element has been adopted to adjust band gap energy.
In the known photodetector, when a semiconductor forming a device receives light having energy of a band gap thereof or more, a photocurrent is generated in the semiconductor device, and light is detected by using the photocurrent.
Recently, there have been attempts to use a plasmon resonance phenomenon to detect light. In [“Nanometer-scale germanium photodetector enhanced by a near-infrared dipole antenna”, Nature Photonics, V2, pp 226-229, 2008] as a paper presented by Tang et al. in Nature Photonics and U.S. Patent Laid-Open Publication 2011/0198499 as a related application, there is an attempt to detect light by positioning a metal nano-rod type of structure and a dipole antenna over and under a Si or Ge semiconductor to increase an avalanche gain operation effect to measure a photocurrent. In this case, the paper describes that the dipole antenna acts to focus light on the semiconductor. Further, [“Photodetection with active optical antennas”, Science, V332, pp 702-704, 2011] as a paper presented by Knight et al. in Science describes that an n-type silicon and an ITO film form a Schottky diode, a gold nano-rod periodically formed therebetween is excited by incident light to form hot electrons, and a portion of the hot electrons contributes to a photocurrent to detect light.
However, in the paper and the patent of Tang et al., light is detected still by using the photocurrent of the semiconductor device. Further, in the paper of Knight et al., the semiconductor device is not used, but light is detected by using the photocurrent flowing between ITO-Au—Si structures. In this case, the photocurrent is shown to be at a pA or nA level.
As described above, the known photodetector is based on the photocurrent excited by light. Accordingly, the wavelength of detected light is inevitably limited.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.